1. Former Channel Habitats of the Sacramento River: Physical and Ecological Processes and Restoration Potential
Presented by Ingrid C. Morken
By G. M. Kondolf, J. Constantine, H. Piegay, I. Morken
J. Levrat, M. Michalkova
Sacramento River Restoration Science Conference
April 10, 2007

2. Former Channel Creation
Former channels, including oxbow lakes, are typically abandoned meander bends, cut off from the main channel.
Two types of cut off mechanisms occur:
Neck cut-off
Chute cut-off

3. Sacramento River Former Channel Habitats: A Typical Evolutionary Pattern
1980
- Main channel occupies meander bend.
- Side channel exists.
1999
Downstream connection grows smaller.
Riparian forest colonizes open areas adjacent to former channel.
1984
- Chute cut-off occurs.
- Upstream plug formed.

4. Sacramento River Former Channel Habitat Value
Provide important habitat different from the main channel, supporting unique vegetation assemblages and wildlife species
Evolutionary stages provide different types of habitat
Important areas for nascent and existing riparian forests

5. STUDY OBJECTIVES
Document and assess former channel evolution processes and patterns
- Field data collection
- Aerial photograph analysis
Identify restoration potential and management implications of former channel evolution trends

6. METHODS FIELD DATA COLLECTION
Measured water depths, water surface elevations, and surficial velocity
Measured fine sediment depths
Assessed granulometric data from sediment cores
AERIAL PHOTOGRAPH ANALYSIS
Measured diversion angle between main and former channels
Delineated, measured various dimensions of former channel sites with time series of aerial photographs

7. STUDY SITES
28 former channel sample sites located between River Miles and 236.8
Former channel sites varied by the following:
- Age
- Hydrologic connectivity to main channel
- Degree of terrestrialization

8. EXAMPLE STUDY SITES
Little Packer Lake
Packer Lake

9. EXAMPLE STUDY SITES
Kopta Slough
La Barranca

10. Hydrologic Connectivity to Main Channel
Water Depths
Ranged from consistently shallow (< 1 m) systems to 3-4 m deep.
Water Surface Elevations
Some former channels more responsive than others, reflecting variations in hydrologic connectivity to main channel.
Surficial Velocity
Velocity responses varied at different river discharges. Greater changes in velocity reflect greater hydrologic connectivity to main channel.
River discharge = 11,300 cfs
River discharge = 26,780 cfs

11. Sediment Depths and Average Annual Sedimentation Rates of Former Channels
Sediment depths ranged from 0 to >5 m. Average approx. 2 m deep.
Sedimentation rates varied from 0 to 18 cm/year.
Average annual sedimentation rate = (cm/year)
Average fine sediment depth (cm)
Age (years)

12. Sedimentation Rate Regression Model

13. Granulometric Data and Relationship to Diversion Angles
Former channels with varying diversion angles reveal different granulometric profiles with depth.
- Greater than 75° dominated by silt and clay above gravel bases.
- Less than 50° shows occurrence of mostly sand to silt
Diversion angle can control formation of sediment plug

14. Granulometric Data and Relationship to Diversion Angles

15. Granulometric Data and Relationship to Diversion Angles

16. Diversion Angle vs. Infilling Rate

17. Aerial Photograph Analysis
Delineated, measured length, width, water surface area, vegetated surface area of sites on 1942, 1962, 1985, and 1999 aerial photographs
Categorized former channels according to size and connection to main channel. Preliminary results suggest that less sinuous former channels with a strong downstream connection tend to have lower sedimentation rates.
Straight (isolated)
Straight (connected)

18. DISCUSSION
Sedimentation rates tend to even out over time, with slower filling former channels catching up to faster filling former channels
A strong relationship occurs between diversion angle and the evolutionary pattern of former channels
Former channel geometric form did not appear to have a strong relationship with sedimentation rates
Former channels show a wide range of hydrologic connectivity to main channel, reflecting evolutionary stage and ecological function

19. MANAGEMENT IMPLICATIONS & RESTORATION POTENTIAL
Long-term management and restoration strategies must consider evolutionary trends
Restoring processes which promote former channel formation are essential. E.g. Riprapped banks inhibit lateral channel migration
Potential restoration sites for riparian forests